/*
 * Copyright (C) 2019 The Dagger Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dagger.example.atm;

import java.util.List;
import java.util.Optional;

/**
 * A text-based command handler.
 */
interface Command {
    /**
     * Processes and optionally acts upon the given {@code input}.
     *
     * @return a {@link Result} indicating how the input was handled
     */
    Result handleInput(List<String> input);

    /**
     * A command result, which has a {@link Status} and optionally a new {@link CommandRouter} that
     * will handle subsequent commands.
     */
    final class Result {
        private final Status status;
        private final Optional<CommandRouter> nestedCommandRouter;

        private Result(Status status, Optional<CommandRouter> nestedCommandRouter) {
            this.status = status;
            this.nestedCommandRouter = nestedCommandRouter;
        }

        static Result invalid() {
            return new Result(Status.INVALID, Optional.empty());
        }

        static Result handled() {
            return new Result(Status.HANDLED, Optional.empty());
        }

        static Result inputCompleted() {
            return new Result(Status.INPUT_COMPLETED, Optional.empty());
        }

        static Result enterNestedCommandSet(CommandRouter nestedCommandRouter) {
            return new Result(Status.HANDLED, Optional.of(nestedCommandRouter));
        }

        Status status() {
            return status;
        }

        Optional<CommandRouter> nestedCommandRouter() {
            return nestedCommandRouter;
        }
    }

    enum Status {
        /**
         * The command or its arguments were invalid.
         */
        INVALID,

        /**
         * The command handled the input and no other commands should attempt to handle it.
         */
        HANDLED,

        // TODO(ronshapiro): maybe call this TERMINATED? If so, maybe this should be called
        // ContinueStatus?
        /**
         * The command handled the input and no further inputs should be submitted.
         */
        INPUT_COMPLETED,
        ;
    }
}
